1. Field of the Invention
The present invention is directed to a process for correcting a differential pressure signal that depends on temperature and static pressure.
2. Description of the Related Art
Generic differential pressure measuring transducers are generally known and described, for example, in German patent publication DE 35 12 529. The electrical signal S, which is generated when the non-electrical variable of differential pressure (dp=p.sub.1 -p.sub.2), representing the difference between a first process pressure p.sub.1 and a second process pressure p.sub.2, is converted into an electrical variable and has, as the result of specified material constants, the intended dependency S.sub.1 =f(dp). In addition, the electrical signal S also has an undesired dependency S.sub.2 =(f(p) on the absolute pressure p=(p.sub.1 +p.sub.2)/2 and a undesired dependency S.sub.3 =(f.theta.) on the temperature .theta. in the differential pressure measuring transducer. Consequently the electrical signal S=f(dp, p, .theta.) is a function of the differential pressure dp, the absolute pressure p and the temperature .theta.. The dependence of the electrical signal S on the absolute pressure p and the temperature .theta. distorts the particular converted measurement value in question. For this reason, the absolute pressure p and the temperature .theta. are described as disturbance variables. Compensating for these disturbance variables in the electrical signal S is the purpose of the invention.
In a sensor arrangement comprising a differential pressure sensor, a temperature sensor and a sensor for static pressure, it is known, as taught by European patent publication EP 0 178 368, to calculate a corrected differential pressure signal using a linear polynomial correction of the three original measurement signals for differential pressure, temperature and static pressure detected by the sensors. To accomplish this, the coefficients of the polynomial function, the weighted functions of temperature and static pressure, are stored in a read-only memory.
It is disadvantageous that this process uses, for the purpose of correction of the differential pressure signal, a measurement value that itself depends on other process parameters. Static pressure, the temperature-dependent measurement value which itself requires correction, is used to correct the differential pressure signal that depends on temperature and static pressure, thereby preventing accurate transformation of the actual differential pressure to the corrected measurement value. Therefore, it is desirable to improve the accuracy of known processes for correcting differential pressure signals that depend on temperature and static pressure.